1. Field of the Invention
The present invention relates to the field of welding. More particularly, the present invention relates to the field of welding where there is a narrow welding gap. Even more particularly, the present invention relates to narrow gap welding using submerged arc welding and gas metal arc welding technologies.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Submerged arc welding (SAW) is common arc welding process. SAW requires a continuously feed consumable solid or tubular electrode. The molten weld and the arc zone are protected from the atmospheric contaminations by being submerged under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium floride, and other compounds. When molten, the flux becomes conductive, and provides a current path between the electrode and the work. This thick layer of flux completely covers the molten metal thus preventing spatter and sparks as well as suppressing the intense ultraviolet radiation and fumes that are part of the SMAW (shielded metal arc welding) process.
SAW is normally operated in the automatic or mechanized mode, however, semi-automatic hand held SAW guns with pressurized or gravity flux speed delivery are available. The process is normally limited to the flat or horizontal-fillet welding positions. Although currents range from 300 to 2000 A are commonly utilized, currents of up to 5000 A have also been used for multiple arcs.
Single or multiple (2-5) electrode wired variation of the process exist. SAW strip-cladding utilizes a flat strip electrode. DC or AC can be utilized, and combinations of DC and AC are common on multiple electrode systems. Constant voltage welding power supplies are most commonly used, however constant current systems in combination with the voltage sensing wire feeder are available. SAW filler material usually is a standard wire as well as other special forms. This wire normally has a thickness of 1/16 inch to ¼ inch. In certain circumstances, twisted wire can be used to give the arc an oscillating movement. This helps fuse the toe of the weld to the base metal.
SAW can be used for various types of material applications, including: carbon steels, low alloy steels, stainless steels, nickel-based alloys and surfacing applications. There are many advantages to using the SAW process including high deposition rates and high operating factors in mechanized applications. Deep weld penetration and minimal welding fumes or arc lights are also advantages to the SAW process. Additionally, minimum welding fume or arc light is emitted. Sound wells are readily made and high speed welding of thin sheets of steel is possible through the SAW process.
Various patents have issued in the past regarding submerged arc welding. For example, U.S. Pat. No. 5,214,265, issued on May 25, 1993 to Pollack, teaches a high-speed, low deposition SAW apparatus and method. The method and apparatus has four electrodes positioned along a line from front to rear. The first of the electrodes is supplied with direct current, and the remaining three electrodes are supplied with alternating current. The direct current electrode generates an arc that penetrates the base metal and initiates a weld. The other electrodes are supplied with alternating current having a 90° current separation between the leading and trailing AC electrodes, and the trailing and middle AC electrodes. Alternating current is supplied between the trailing and middle AC electrode, having a 180° current separation. The AC electrodes combine to generate an arc that deposits a filler and shapes the weld.
U.S. Pat. No. 5,140,140, issued on Aug. 18, 1992 also to Pollack, describes a method and apparatus of submerged arc welding with electrodes in tandem. The method and apparatus uses five electrodes having direct current connecting to one electrode and alternating current connected to the other four electrodes. The electrodes are aligned in a row with predetermined angles to the direction of the weld. Alternating current is supplied to the electrodes so that a 90° phase difference is applied to adjacent electrodes and a 180° phase difference is applied between alternating electrodes. With such power application and the electrical connections of the electrodes, the welding process has a more stable weld puddle that suppresses welding defects at higher speeds than previously achievable.
U.S. Pat. No. 3,859,495, issued on Jan. 7, 1975 to Takahashi et al., describes a submerged-arc welding machine. The submerged-arc welding machine has a welding head pivoted to a frame of the machine so as to be rockable across the seam of a workpiece being welded. Additionally, the machine has a vertically-movable oscillation mechanism with an eccentric cam engaging the welding head for causing the welding head to rock across the seam as the cam rotates. Further included is an oscillation amplitude adjusting device for moving the oscillation mechanism as well as the cam vertically, whereby the axis of rotation of the cam is adjustable relative to that point on the frame about which the welding head pivots to adjust the amplitude of the rockable movement of the welding head.
Various patents have also issued in the past relating to narrow gap or narrow groove welding. For example, U.S. Pat. No. 4,254,322, issued on Mar. 3, 1981 to Asano, describes a narrow weld groove welding process and apparatus using gas metal arc welding. In this process, a bare welding wire is fed into a weld groove defined between the opposed surfaces of two pieces of metals for producing a metal arc therein for welding. In this process, a welding wire is subjected to a plastic deformation of a wave form, before being fed into a nozzle hole provided in a contact tip. Then, the wire is fed into a nozzle hole, while maintaining elasticity tending to cause waving. The tip of a welding wire being fed through a nozzle exit is automatically waved between the opposed surfaces of metals to be joined, with the tip of wire being alternately faced in the opposite direction in response to the weaving motion thereof.
U.S. Pat. No. 3,576,966, issued on May 4, 1971 to Sullivan, describes a patent similar to the Asano patent, but uses two axes and again is limited to gas shielded welding. In this patent, a welding wire of serpentine form is fed into an electric arc in a narrow gap between workpieces to be joined. The wire passes through a contact tube which is sheathed in electrical insulation to avoid short-circuiting to the workpieces. The serpentine form of the wire serves to direct the arc toward one side of the gap or the other in periodic oscillations as the electrode is moved lengthwise of the gap from one end to the other. The seam is built up layer-by-layer in repeated passes of the electrode.
Patents have also issued which deal with narrow groove welding using submerged arc welding technologies. For example, U.S. Pat. No. 4,442,334 issued on Apr. 10, 1984 to Lux et al., describes a device for feeding welding wire in a submerged arc welding operation in which there is a narrow gap between workpieces which are to be welded together. A guide support has a plurality of spaced-apart welding wire straightening roller assemblies mounted thereon. The roller assemblies are in a position at selected angles relative to each other around and in engagement with the welding wire and define a feed guide path for the passage of the welding wire between the rollers of each assembly. A welding head is pivotally mounted on a support for pivotal movement transverse to the welding direction. The head includes a welding guide and a carrying guide which together define tongs of the head. The tongs are mounted on the support for pivotal movement toward and away from each other. Tongs carry a plurality of guide shoes which define a continuing guide path for the welding wire received from the welding wire feed guide and deliver it to the welding zone between the workpieces. A contact piece associated with the current carrying guide provides current for the welding operation. The construction includes three straightening roller assemblies with three roller assembly elements which are rotatable relative to each other in a direction around the periphery of the wire which they cooperate to guide and straighten. The welding head includes a welding guide blade and a current carrying guide blade which are pivotally mounted on a hinge bolt. Straightening roller units are carried in a cylindrical roller housing on the support. Each of the roller housings has a substantially tubular shell which is designed with an upper inside recess and with a lower centering extension to be snugly fitted into the recess of each following roller housing.
Gas metal arc welding (GMAW) is another type of welding process. GMAW, sometimes referred to by subtypes metal inert gas welding or metal active gas welding, is a semiautomatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun. A constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. There are four primary methods of metal transfer in GMAW, referred to as globular, short circuiting, spray, and pulsed-spray. Each of these methods have stage properties and corresponding advantages and limitations.
Originally developed for welding aluminum and other non-ferrous materials in the 1940's, GMAW was soon applied to steels because it allowed for lower welding time compared to other welding processes. The cost of inert gas limited its use in steels until several years later, when the use of semi-inert gases such as carbon dioxide became common. Further developments during the 1950's and 1960's gave the process more versatility and, as a result, it became a highly used industrial process. Today, the automobile industry in particular uses GMAW almost exclusively. Unlike welding processes that do not employ a shielding gas, such as shielded metal arc welding, GMAW is rarely used in outdoors or in other areas of air volatility. A related process, flux cord arc welding, often does not use a shielding gas, instead employing a hollow electrode wire that is filled with flux on the inside.
Various patents in the past have issued relating to gas metal arc welding. For example, U.S. Pat. No. 4,301,355 issued on Nov. 17, 1981 to Kimbrough et al., describes a gas metal arc welding system. In the system, power is delivered to the welding arc from a constant-current rapid-response power supply controllable to maximize arc stability particularly in out-of-position welding operations. A first control modulates the output current from the power supply between a high value close to the maximum output value and a minimum value just sufficient to maintain the welding arc. The modulation is effected at a given frequency appropriately adjusted in accordance with the electrode material and diameter to maintain optimum spray metal transfer in the welding arc. A further control is effected by pulse width modulating the output from the power supply in accord with a set-in current programmed signal which is compared with a current feedback signal or, alternatively, a set in voltage programmed signal which is compared with a voltage feedback signal. This latter control provides for operation of the power supply in a constant current control mode or, alternatively, a constant voltage control mode. Still further control of the power in the welding arc is effected by pulsing the current between base and peak levels at a relatively low frequency which enables control of the weld puddle in out-of-weld positions.
U.S. Pat. No. 4,529,863, issued on Jul. 16, 1985 to Lebel, describes a GMAW method. A consumable wire electrode is held within and fed through the tubular contact tip of a continuous feed-type welding gun having a tubular nozzle surrounding and extending beyond the tip. A shielding gas, formed of unique ratios of a minor proportion of a carbon dioxide and oxygen mixture combined with a major proportion of an argon and helium mixture, is flowed in a substantially longitudinally laminar pattern between the nozzle and contact tip and along the electrode extension from the tip. The contact tip is cooled, and sufficiently high power electrical current is passed through the contact tip and electrode extension to produce the arc and to melt the end of the electrode into molten drops for short-circuiting or for spray transfer of the drops to the weld deposit. The electrode extension is pre-heated by maintaining a long electrode extension or stick-out beyond the contact tip end, with a substantial portion of the extension recessed within the nozzle.
It is an object of the present invention to provide a narrow gap welding apparatus and method that reduces the volume of weld metal.
It is another object of the present invention to provide a narrow gap welding apparatus and method that reduces the preparation requirements for the weld site.
It is yet another object of the present invention to provide a narrow gap welding apparatus and method that does not require cutting a V-shape into the material to be welded together.
It is a further of the present invention to provide a narrow gap welding apparatus and method that does not require beveling of parts.
It is an object of the present invention to provide a narrow gap welding apparatus and method that can be used in a narrower groove.
It is yet another object of the present invention to provide a narrow gap welding apparatus and method that requires fewer welding passes to complete the weld.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.